Dental repair material

ABSTRACT

The invention is directed to an improved dental composition useful in the repair of cavities, apex repairs, root perforations and root canals. Disclosed is a dental composition and dental composition additive which have improved handling characteristics, for example improved viscosity and setting time. The addition of effective amounts of a modified cellulose and calcium chloride to available dental repair compounds, such as mineral trioxide compound, results in the improved dental composition without affecting the other characteristics of the dental repair compound.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 11/473,536, filed Jun. 23, 2006, which claims priority toProvisional U.S. Patent Application No. 60/693,268, which was filed onJun. 23, 2005, both of which are incorporated by reference in theirentireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is related to dental repair materials. Specificallyimproved MTA (mineral trioxide aggregate) with improved handling andsealing properties.

2. Summary of the Related Art

Various compounds have been used as dental fill materials for cavitiesand root canal therapy. These include Amalgam, Reinforced ZincOxide-Eugenol (IRM and Super EBA), Composite Resins and Mineral TrioxideAggregate (MTA) and Portland Cement, herein after referred to generallyas “Dental Repair Compound”.

The attributes generally sought for root-end filling material includethe ability to 1) seal the apical portion in three dimensions, 2) bewell tolerated by the periradicular tissues with no inflammatoryreactions, 3) be non-toxic, 4) not promote, and preferably inhibit, thegrowth of pathogenic organisms, 5) stimulate the regeneration of normalrepiradicular tissues, 6) not be affected by moisture in either the setor unset state, 7) not be absorbable by the body within the confines ofthe tooth, but excess should be absorbable, 8) be dimensionally stableand should not expand, contract, or flow in any direction when set, 9)not corrode or be electrochemically active, 10) not stain the tooth orthe periradicular tissues, 11) be easy to mix and insert, 12) be easilydistinguishable on radiographs, and 13) adhere or bond to the toothwithout the need of undercuts.

MTA has been demonstrated to have diverse applications for all fields ofdentistry and appears to fulfill most characteristics of an ideal cementdue to its unique properties such as tissue compatibility, marginaladaptation, sealing ability, hydrophilic properties, and the capacity tostimulate hard tissue formation. These properties have allowed MTA to beindicated for the following endodontic procedures: Pulp Capping,Apexification, Perforation repair and other Miscellaneous uses.

Pulp Capping—In 1929, Hess reported a pulpotomy technique using calciumhydroxide. Until recently, these calcium hydroxide-based materials havefound widespread use in traditional vital pulp therapy and have been themainstay for the protection of exposed dental pulps. The healing processof the dental pulp following a pulpotomy or a direct pulp cap ischaracterized by the formation of a hard tissue bridge with themaintenance of a vital subjacent pulp tissue free from chronicinflammatory cells. Recently, MTA has been approved by the FDA andrecommended for direct pulp capping. MTA's mechanism of action isthought to be similar to that of calcium hydroxide. MTA has calciumoxide that mixes with water to form calcium hydroxide. The reaction ofthe calcium from the calcium hydroxide with the carbon dioxide from thepulp tissue produces calcite crystals. These calcite crystals arethought to be the initiating factor in the induction of a hard tissuebarrier. Seux (1) observed a rich extracellular network of fibronectinin close contact with these crystals and concluded that both wereintegral in the initiating steps in the formation of a hard tissuebarrier. Tziafas (2) concluded that MTA was able to induce cytologicaland functional changes in pulpal cells, resulting in the formation offibrodentin at the surface of a mechanically exposed dental pulp.

Human studies have shown MTA to cause less pulpal hyperemia,inflammation, and necrosis when compared to calcium hydroxide. In astudy performed by Aeinehchi, (7) MTA induced a thicker dentinal bridgein third molars and was found to be associated with an intactodontoblastic layer more often than with calcium hydroxide. Additionalreasons MTA is an effective pulp capping material is its ability toeffectively seal the dentin-material interface to prevent bacterialcontamination, it is nonresorbable, proven biocompatibility, andbeneficial alkaline properties (25; 26; 27). Because of this, MTA isalso recommended for treatment of traumatically exposed pulps for thetreatment of complicated crown fractures (8).

Apexification—The traditional protocol in the treatment of necroticimmature teeth is through apexification using calcium hydroxide. In1959, Granath was the first to describe the utilization of calciumhydroxide for apical closure. In 1966, Frank mainstreamed theapexification technique and was credited as being the first to use thismodality (9). This methodology consists of multiple appointmentsexchanging calcium hydroxide as the intracanal medicament to induce anapical hard tissue barrier ultimately to control the root canal fillingmaterial. The calcium hydroxide is changed every 3 months until there isevidence of apical barrier formation. The most important problem withthe classic apexification technique with calcium hydroxide is theduration of therapy, which can last from 3 to 24 months (9; 10). Duringthis time frame the root canal is susceptible to reinfection due to thedifficulty in maintaining a temporary restorative material thatadequately seals the access opening. The root is also at risk tofracture due to the long treatment time required for apical barrierformation.

MTA treatment of these cases allows for a single treatment of immatureteeth as an option. The MTA apical plug technique, a one-step obturationafter short canal disinfection with calcium hydroxide is designated tocreate an artificial stop to the filling material. The physicalcharacteristics of MTA provide advantages over the traditional calciumhydroxide technique. MTA apexification cases can be restored inapproximately two weeks as opposed to traditional calcium hydroxidetherapy, which could take several months. MTA provides excellentmarginal adaptation to prevent leakage and the material isnon-resorbable. In 1996, Buchanan first recommended the use of MTA forone-appointment apexification by placing an apical matrix offreeze-dried demineralized bone followed by condensation of MTA (11).Witherspoon also recommends a technique for one-visit apexification.This technique advocates filling the apical to middle third with MTA,with the remainder of the canal system to be restored with a corematerial to reinforce the thin walls of the root (12). Giulianidescribed using MTA as an apical plug in teeth with necrotic pulps andopen apices. His technique advocated the use of calcium hydroxidetreatment for one week prior to placement of MTA as an apical plug withsubsequent obturation of the canal system. At recall, the clinicalsymptoms and teeth with periapical lesions had resolution within 6-12months (13). Hachmeister, in an MTA displacement study, concluded therewas a significant greater resistance to force with a 4 mm thickness ofMTA, regardless of calcium hydroxide use. Thus, the ideal recommendedthickness of the apical plug was shown to be 4 mm, in order to resistdisplacement of the material (14).

Perforation Repair—In dentistry, procedural accidents such as root orfurcal perforations can occur during root canal therapy, post spacepreparation, or as a consequence of internal resorption. Studies haveshown that these perforations predispose periradicular tissues tochronic inflammation and promote the advancement of periodontalattachment loss, ultimately causing the loss of the tooth (15). Inglereported that perforations were the second greatest cause of endodonticfailure and accounted for 9.6% of all unsuccessful cases (16).

The repair of perforations can be problematic due to extrusion of therepair filling material, improper hemorrhage control, and the ability ofthe material to adequately seal the perforation site. MTA's uniquephysical characteristics allowing for superior marginal adaptation andsealing ability in hematic environments along with itsosteo/cementoconductive attributes make it an excellent material forperforation repair (28; 29; 30; 31). The inherent hydrophilic propertiesof MTA allow the repair material to set in a wet environment andadequately seal the perforation site. In 1993, Lee reported the first invitro study investigating the sealing ability of MTA for repair oflateral root perforations. The authors were able to demonstrate thatmoisture of the surrounding tissue acted as an activator of the chemicalreaction and did not pose a risk with its use in a moist environment.They were also able to demonstrate that overextrusion of the materialinto the perforation site occurred mostly in the IRM group, followed bythe amalgam group and then MTA. Lee concluded that the hydrophilicpowder absorbs moisture and allows for minimal condensation force, thusdecreasing the chance of overextrusion of the material (49). Sluykconcluded that the presence of moisture in the perforation site duringplacement was advantageous in aiding adaptation of MTA to the walls ofthe perforation (86).

Histologic repair of the perforation is possible with MTA. Pitt Ford etal. demonstrated using an in vitro canine model, that cementum has beenwas produced over MTA repairing perforations in the absence ofinflammation. Based on these results, Pitt Ford recommended the use ofMTA for immediate perforation repair (19). Holland also demonstrated noinflammation associated with repair of lateral root perforations withMTA over a 180 day observation period and that there was evidence ofcementum deposition in the majority of specimens (20). Recent studiesperformed to evaluate the clinical efficacy of MTA to seal both furcaland lateral perforations have only validated MTA as the material ofchoice in perforation repair (88-90).

Miscellaneous Uses—Additional uses for MTA have also been suggested. Ina study performed by Cummings, MTA was compared to other materials andevaluated as an isolating barrier for internal bleaching. MTAdemonstrated the least amount of leakage compared to IRM and zincphosphate. It was concluded that this material can be used as aneffective isolating barrier for internal bleaching (21).

There have been several case reports documenting alternative uses forMTA. Hsiang-Chi presented a successful case report demonstrating therepair of perforating internal resorption with MTA. A partial pulpotomywas performed, and the material was placed adjacent to the exposed pulp.Teeth were extracted after 6 months. Histological exam of the teethshowed continuous dentin bridge formation without inflammation 6 monthsafter initial treatment (93). O'Sullivan (23), in another case report,demonstrated obturation of the canal system with MTA in a retainedprimary mandibular second molar where there was no succendaneous toothpresent. Eidelman et al. found clinical and radiographic success as adressing material following pulpotomy in primary teeth, suggesting MTAas a possible alternative to formocresol in primary teeth (24).

Presently, dental materials, such as e.g., MTA, Portland cement, aredifficult to handle due to viscosity and slow setting times. Thesematerials have low viscosity and therefore require special equipment toadminister into small or tortuous areas in the patient's mouth.

U.S. Pat. Nos. 5,415,547, and 5,769,638 titled “Tooth Filling Materialand Method of Use.” Teach the use of Portland Cement as a dental repairmaterial for apicoectomy, a tooth cavity, correction of rootperforation. Those patents also teach a method of performing aapicoectomy, a method for filling teeth and a method for sealing rootperforations. It has also been observed that Portland Cement has similarproperties to MTA as a dental repair compound.

International Patent Application WO 2005/039509 A1, titled “A DentalComposite Material and Uses Thereof” Teaches using a viscosity enhancingadditive in Portland Cement. The application also teaches using the sameviscosity enhancing substance to improve MTA as a workable dental repairmaterial. However the description suggested enhancement of MTA. Theviscosity enhancing substance is Polyvinyl alcohol, cellulose, cellulosederivatives, polyethylene oxide, natural gums, and/or aqueous claydispersion.

The following references are cited throughout this section using therelated parenthetical numbering system. The references are incorporatedherein by reference. Applicant reserves the right to challenge theveracity of statements made therein.

1) Seux D, Regad C, Magloire H, Holz J. A model of an in vitrobiological assay controlled by immunofluorescence and scanning electronmicroscopy. J Biol Buccale. 1991; 19:147-53.

2) Tziafas D, Pantelidou O, Alvanou A, Belibasakis G, Papadimitriou S.The dentinogenic effect of mineral trioxide aggregate (MTA) inshort-term capping experiments. Int Endod J 2002; 35:245-54.

3) Pitt Ford T R, Torabinejad M, Abedi H R, Bakland L K, Kariyawasam SP. Using mineral trioxide aggregate as a pulp-capping material. J AmDent Assoc 1996; 127:1491-4.

4) Faraco I M, Jr., Holland R. Response of the pulp of dogs to cappingwith mineral trioxide aggregate or a calcium hydroxide cement. DentTraumatol 2001; 17:163-6.

5) Junn D J, McMillan P, Bakland L K, Torabinejad M. Quantitativeassessment of dentin bridge formation following pulp capping withMineral Trioxide Aggregate (MTA).[Abstract #29] J Endod 1998; 24:278.

6) Dominguez M S, Witherspoon D E, Gutmann J L, Opperman L A.Histological and scanning electron microscopy assessment of variousvital pulp-therapy materials. J Endod 2003; 29:324-33.

7) Aeinehchi M, Eslami B, Ghanbariha M, Saffar A S. Mineral trioxideaggregate (MTA) and calcium hydroxide as pulp-capping agents in humanteeth: a preliminary report. Int Endod J 2003; 36:225-31.

8) Bakland L K. Management of traumatically injured pulps in immatureteeth using MTA. J Calif Dent Assoc 2000; 28:855-8.

9) Frank A. Therapy for the divergent pulpless tooth by continued apicalformation. J Am Dent Assoc 1966; 72:87-93.

11) Buchanan L S. One-visit endodontics: a new model of reality. DentToday 1996; 15:36, 8, 40-3.

12) Witherspoon D E, Ham K. One-visit apexification: technique forinducing root-end barrier formation in apical closures. Pract ProcedAesthet Dent 2001; 13:455-60.

13) Giuliani V, Baccetti T, Pace R, Pagavino G. The use of MTA in teethwith necrotic pulps and open apices. Dent Traumatol 2002; 1 8:217-21.

14) Hachmeister D R, Schindler W G, Walker W A, 3rd, Thomas D D. Thesealing ability and retention characteristics of mineral trioxideaggregate in a model of apexification. J Endod 2002; 28:386-90.

15) Seltzer S, Sinai I, August D. Periodontal effects of rootperforations before and during endodontic procedures. J Dent Res. 1970;49:332-9.

16) Ingle J I. A standardized endodontic technique utilizing newlydesigned instruments and filling materials. Oral Surg Oral Med OralPathol. 1961; 14:83-91.

17) Lee S J, Monsef M, Torabinejad M. Sealing ability of a mineraltrioxide aggregate for repair of lateral root perforations. J Endod1993; 19:541-4.

18) Sluyk S R, Moon P C, Hartwell G R. Evaluation of setting propertiesand retention characteristics of mineral trioxide aggregate when used asa furcation perforation repair material. J Endod. 1998; 24:768-71.

19) Pitt Ford T R, Andreasen J O, Dorn S O, Kariyawasam S P. Effect ofvarious zinc oxide materials as root-end fillings on healing afterreplantation. Int Endod J 1995; 28:273-8.

20) Holland R, Filho J A, de Souza V, Nery M J, Bemabe P F, Junior E D.Mineral trioxide aggregate repair of lateral root perforations. J Endod.2001; 27:281-4.

21) Cummings G R, Torabinajad M. Mineral Trioxide Aggregate (MTA) as anisolating barrier for internal bleaching. [Abstract #53] J Endod. 1995;21:228.

22) Hsieng H C, Cheng Y A, Lee Y L, Lan W H, Lin C P. Repair ofperforating internal resorption with mineral trioxide aggregate: a casereport. J Endod. 2003; 29:538-9.

23) O'Sullivan S M, Hartwell G R. Obturation of a retained primarymandibular second molar using mineral trioxide aggregate: a case report.J Endod. 2001; 27:703-5.

24) Eidelman E, Holan G, Fuks A B. Mineral trioxide aggregate vs.formocresol in pulpotomized primary molars: a preliminary report.Pediatr Dent. 2001; 23:15-8.

25) Torabinejad M, Watson T F, Pitt Ford T R. Sealing ability of amineral trioxide aggregate when used as a root end filling material. JEndod. 1993; 19:591-5.

26) Torabinejad M, Pitt Ford T R, McKendry D J, Abedi H R, Miller D A,Kariyawasam S P. Histologic assessment of mineral trioxide aggregate asa root-end filling in monkeys. J Endod 1997; 23:225-8.

27) Torabinejad M, Hong C U, McDonald F, Pitt Ford T R. Physical andchemical properties of a new root-end filling material. J Endod 1995;21:349-53.

28) Pitt Ford T R, Torabinejad M, McKendry D J, Hong C U, Kariyawasam SP. Use of mineral trioxide aggregate for repair of furcal perforations.Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1995; 79:756-63.

29) Koh E T, Torabinejad M, Pitt Ford T R, Brady K, McDonald F. Mineraltrioxide aggregate stimulates a biological response in humanosteoblasts. J Biomed Mater Res. 1997; 37:432-9.

30) Moretton T R, Brown C E, Jr., Legan J J, Kafrawy A H. Tissuereactions after subcutaneous and intraosseous implantation of mineraltrioxide aggregate and ethoxybenzoic acid cement. J Biomed Mater Res2000; 52:528-33.

31) Thompson T S, Berry J E, Somerman M J, Kirkwood K L. Cementoblastsmaintain expression of osteocalcin in the presence of mineral trioxideaggregate. J Endod 2003; 29:407-12.

SUMMARY OF THE INVENTION

The inventors have made the surprising discovery that the addition ofdivalent-cationic halogen salt and derivatives of cellulose polymers todental repair compounds results in dental repair compositions havingimproved handling properties, which enables more effective treatment ofvarious indications of use. Those improved handling properties includeincreased viscosity and shortened setting time. Thus, the invention isdirected to compositions, treatment methods, and manufacturing processesfor improved dental repair compositions and dental repair procedures.

In one embodiment, the invention is drawn to a dental repaircomposition, comprising a dental repair compound, such as for examplebut not limited to Portland cement and mineral trioxide aggregate(“MTA”), a divalent cation halogen salt (e.g., calcium chloride,magnesium chloride, and the like), and a polymer thickening agent, suchas a cellulose derivative polymer like methyl-cellulose or the like. Ina preferred aspect, the divalent cation halogen salt is calcium chlorideand the polymer thickening agent is methyl-cellulose. However, theinventors envision that other salts and polymers, which have similarproperties to CaCl₂ and methyl-cellulose, may also be used as additivesto the dental repair compounds to produce the same improved handlingproperties (supra). Concentration ranges for the divalent cation halogensalt can be from as low as 0.1% by weight to as high as 20% by weight.Likewise, the concentration range for the polymer thickener can be fromas low as 0.1% by weight to as high as 20% by weight. In a morepreferred embodiment, the salt is CaCl₂ at a concentration ofapproximately 2% by weight and the polymer thickener is methyl-celluloseat a concentration of approximately 1%. However, the inventors envisionthat the relative amounts of CaCl₂ and methyl-cellulose may be alteredoutside of these ranges and values, so long as the therapeuticproperties of the dental repair compound are not significantlycompromised.

In another embodiment, the invention is drawn to a compound additive,which can be added to a dental repair compound (supra). The compoundadditive is a gel or solution that consists essentially of the divalentcation halogen salt and polymer thickening agent. To produce theimproved dental repair composition, the practitioner would mix thecompound additive with the dental repair compound to produce the workingimproved dental repair composition prior to application to the patient.Preferably, the compound additive consists essentially of CaCl₂ andmethyl-cellulose, both of which are represented at concentrations higherthan their respective final concentrations in the working improveddental repair composition.

In another embodiment, the invention is drawn to methods of producingthe improved dental repair composition and compound additives (supra).In one particular preferred aspect, calcium chloride is weighed out inan amount representing approximately 2% of the final composition weight.The calcium chloride is added to water for a 3:1 powder to water ratio(by weight). The solution can be divided in half, half of which isheated to 80° C. The methyl-cellulose is weighed out in an amountrepresenting approximately 1% or 2% of the final composition weight. Themethyl-cellulose is added to the half of the calcium chloride solutionthat was heated to 80° C. To this mixture, the other half of the calciumchloride solution (at room temperature) is added to the warm solutionand stirred until all of the solid material is in solution. This mixtureis then chilled to 0° C. to allow the mixture to thicken. The solutionis stirred for about 30 minutes to produce a homogeneous gel. This gelis a compound additive, which may then be added to the dental repaircompound (e.g., MTA, Portland cement) to produce the improved dentalrepair composition.

In another embodiment, the invention is drawn to methods of effectingdental repairs using the improved dental repair compositions described(supra). Those dental repairs include but are not limited to filling atooth cavity, treating tooth decay, performing root canal therapy,apicoectomy, and sealing a root perforation.

In yet another embodiment, the invention is drawn to a kit useful in thepractice of dental repair, said kit comprising a packaged dental repaircompound (e.g., Portland cement, MTA), a packaged compound additive(supra), and a set of instructions describing how to mix (e.g., in whatproportions) the dental repair compound and compound additive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Root-end filling diagrams and evaluation scores: which 0=no dyepenetration observed, 1=dye penetration observed up to ½ of the cavitydepth, 2=dye penetration observed between ½ but not beyond root-endfilling material placement, 3=dye penetration observed beyond thefilling material and into the canal system.

FIG. 2. depicts the chemical shrinkage apparatus.

FIG. 3. depicts the receiving container and washout apparatus.

FIG. 4 depicts methylene blue penetration beyond the material dentininterface for amalgam.

FIG. 5 shows no methylene blue penetration noted for MTA.

FIG. 6 shows no methylene blue penetration noted for CMMTA.

FIG. 7 shows the graph illustrating the chemical shrinkage over 168hours for samples 1 through 6.

FIG. 8 shows the Graph Illustrating the chemical shrinkage over 8 hoursfor samples 1 through 6.

DETAILED DESCRIPTION

The following example discloses a single preferred embodiment of theinvention. It is meant merely to illustrate the invention and not tolimit the invention. The skilled artisan in the practice of thisinvention will readily recognize that substitutions and alterations canbe made while remaining within the metes and bounds of the invention,which are set forth in the claims that follow.

Recently, the inventors herein demonstrate improved characteristics ofMTA (PROROOT Dentsply Tulsa Dental, Tulsa, Okla.) through the additionof 1% methylcellulose (MC) and 2% calcium chloride (CaCl₂) into itsparent cement. The inventors observed that the handling characteristicswere vastly improved while the compressive strength of MTA with theadditives was not significantly affected and the setting time of MTAwith the additives was significantly shorter than the MTA control. Thisobservation also brought about questions on whether the chemicaladditives have significantly altered any inherent physical propertiescrucial to MTA's success as an ideal dental cement. Therefore, thisexample describes the physical properties, (marginal leakage, chemicalshrinkage, cement solubility, and washout resistance) of chemicallymodified MTA (1% MC+2% CaCl₂ in MTA/H₂O) and compare it to unalteredMTA.

Four different tests were designed and employed to assess marginalleakage, chemical shrinkage, cement solubility, and washout resistancebetween the unaltered MTA and chemically modified MTA (CMMTA) to ensurethat the added chemicals have not deteriorated the aforementionedproperties of MTA.

Dye leakage results demonstrated no significant difference between CMMTAand MTA samples. In addition, there was significantly less leakagebetween the CMMTA and MTA groups compared to amalgam. Chemical shrinkageresults reported no significant difference between any of the groups(1-6) at any of the designated timeframes (T₁, T₂, T₃, T₂₄, and T_(w)).More importantly, there was no significant difference in mean chemicalshrinkage between CMMTA and MTA samples at any of the designated timeintervals of the specimens. Cement solubility results revealed nosignificant difference between CMMTA and MTA groups. Furthermore,results demonstrated no significant difference between weights of thetest materials at any designated time intervals (T₁, T₇, T₂₁). Modifiedwashout tests indicated a significant difference observed between groups1-3. However, there were no significant differences noted between CMMTAand MTA groups.

In conclusion, the data presented in this research confirm that theaddition of 1% MC+2% CaCl₂ into MTA does not deleteriously alter any ofthe parent cement's physical properties (marginal leakage, chemicalshrinkage, cement solubility, and washout resistance) and that CMMTAperformed as well or better than MTA in all of the above testsconducted.

EXAMPLE Modified MTA

As of 2005, there have been some 150 articles published regardingMineral Trioxide Aggregate's (MTA) composition, properties,biocompatibility, and indications for use. MTA has become the materialof choice for an array of endodontic applications, including vital pulptherapy, apexification, perforation repair, as well as a root-endfilling material. Any root-end filling material should have the abilityto seal the root canal from bacterial and chemical invasion as well asbe biocompatible, prevent periradicular tissue irritation, and ideallyfavor regeneration of the involved tissues to their prediseased status(1).

MTA has been demonstrated to meet many of the ideal properties of aroot-end filling material as described by Gartner and Dom (2). MTA isdifferent from other root-end filling materials currently in use,(Super-EBA, IRM, Amalgam, and composite resin-based materials). Both invitro and in vivo studies have consistently demonstrated this materialto be equal or superior in terms of its biocompatibility (3-9), marginaladaptation (10) and sealing abilities, (11-13), even in the presence ofblood and moisture (14).

MTA is a chemical mixture of three powder ingredients: Portland cement(75%), bismuth oxide (20%), and gypsum (5%) (15). These powders consistsof fine trioxides and other hydrophilic particles, that upon mixing withsterile water, results in a wet, sandy consistency that sets in thepresence of moisture in approximately 165 minutes. Hydration of thepowder results in the formation of a colloidal gel with an initialsetting pH of 10.2, which increases to 12.5 after 180 minutes. Anelemental analysis of MTA revealed an overall composition of MTA as58.9% Ca, 20.1% Bi, 9.4% Si, 2.1% Al, 2.7% S, 4.4% Fe, with traceamounts of Cr, Ni, and Pb (16).

The unique composition of MTA often makes it hard to use, especially inregions with difficult access. According to Lee (17), MTA is a difficultmaterial to handle due to its granular consistency, slow setting time,and initial looseness. Once the mixture starts to dry, it loses itscohesiveness and becomes unmanageable. Delivery of MTA has focusedmainly on carrier and syringable-type devices to simplify placement ofthe material, however, each still has its own set of problems. Thedevices can become easily clogged and can be difficult to use due tolocation and access of the surgical site.

Recent modifications to MTA has been studied and shown to improve thehandling characteristics (18). 1% methylcellulose (MC) was added as ananti-washout additive to enhance handling characteristics and provide amore cohesive user-friendly material. This additive does have drawbacks,including decreased compressive strength due to voids entrapped in thecement and longer setting times. To offset these drawbacks, 2% CaCl₂ wasincorporated as an accelerator to decrease the setting time. Theinventors observed that the compressive strength with the additives wasnot significantly affected compared to MTA at 24 hours and 3 weeks(Table 1) while setting time of MTA with the additives was significantlyshorter than the MTA control (Table 2).

TABLE 1 Compressive strength 24 hrs 3 wks 1% MC + 2% CaCl₂ in MTA 25.5 ±4 MPa 29.1 ± 6.4 MPa MTA (control) 26.4 ± 6 MPa 30.4 ± 12.8 MPa.

TABLE 2 Setting time Minutes 1% MC + 2% CaCl₂ in MTA  57 ± 3 MTA(control) 202 ± 3

Materials and Methods—All chemically modified MTA (CMMTA) samples wereprepared as described by Ber (18). Briefly, CaCl₂ (PCCA, Houston, Tex.)equal to 2% of the sample weight was added to distilled water and mixedinto solution. Half of the solution was placed on a hot plate were thetemperature of the solution was raised to 80° C. 1% MC (Sigma, St.Louis, Mo.) was added to the warmed solution and stirred to wet theparticles. The remainder of the room temperature solution was added andthen stirred until all of the powder was in solution. It was then storedat 0° C. for 20 minutes to allow for the mixture to thicken. Thesolution was then mechanically stirred for 30 minutes to create ahomogenous gel. This solution was then added to MTA at a 0.33water/cement ratio generate a chemically modified MTA cement. Allconventional MTA samples were mixed with distilled water according tomanufacturer's instructions, using a powder to water ratio of 3:1.

Dye Leakage—Forty-one extracted, human, single-rooted maxillary incisorswere collected and stored in 10% formalin. The clinical crowns weredecoronated at the cementoenamel junction (CEJ) with a #557 carbide burin a highspeed handpiece with water coolant. Working length wasdetermined by subtracting 0.5 mm from the length at which a #10 K fileexited the apical foramen. Teeth were prepared using rotaryinstrumentation to a master apical file (IAF) size 40/04 withnickel-titanium (NiTi) ProFile (Tulsa Dental Products, Tulsa, Okla.)instruments via modified crown-down technique in conjunction with RCPrep (Premier, King of Prussia, Pa.) and 5.25% NaOCl⁻ (Clorox; CloroxCo., Oakland Calif.). The canals were dried with paper points andsamples were obturated immediately with Roth Root Canal Cement 801 Elitegrade (Roth International Ltd., Chicago, Ill.) and thermoplasticizedgutta-percha utilizing an Obtura II (Obtura/Spartan USA, Fenton, Mo.)unit set at 200° C. and expressed in one continuous movement. Canalswere then compacted with an S Kondensor plugger (Obtura/Spartan USA,Fenton, Mo.) and coronal access openings sealed with IRM (ID Caulk,Milford, Del.).

All roots were then stored at 37° C. and 100% humidity for 1 week.Apical root resections were performed on all roots by removing 3 mm ofeach apex at 90 degrees to the long axis of the tooth with a #169fissure bur using a highspeed handpiece with water coolant. A 3 mmroot-end cavity preparation was performed using ultrasonics (SpartanUSA, Fenton, Mo.) and KIS tips (Obtura/Spartan USA, Fenton, Mo.) undersurgical microscope (Global Surgical Corp., St. Louis, Mo.) at 9.times.magnification. Two coats of nail polish were applied to the entiresurface of each root except where the root-end filling was to be placed.

Teeth were randomly assigned to two groups of 15 roots each. Group 1 wasretrofilled with MTA (PROROOT, Dentsply Tulsa Dental, Tulsa, Okla.).Group 2 with chemically modified MTA, (1% MC+2% CaCl₂ in MTA). Anadditional 5 roots (Group 3) were filled with high copper amalgam (TytinAmalgam, Kerr Mfg. Co., Romulus, Mich.) without cavity varnish. Eachmaterial was condensed into their respective preparation sites using anS Kondensor plugger. Three instrumented roots with retrogradepreparations and no root-end fillings served as positive controls whilethree roots were instrumented and obturated with gutta-percha andsealer. Entire root surfaces covered with two coats of nail polish wereused as negative controls.

All roots were then stored in 1% methylene blue for 72 hours. The rootswere rinsed with distilled water and nail polish removed. Teeth weresectioned buccolingually using a 169 tapered fissure bur in a highspeedhandpiece and fractured using a Woodson instrument. Dye penetration wasevaluated under surgical microscope (Global Surgical Corp., St. Louis,Mo.) at 9× magnification.

The presence of dye penetration through the material/dentin interfacewas scored on a four-point scale as shown in FIG. 1, in which 0=no dyepenetration observed, 1=dye penetration observed up to 1 of the root-endfilling material, 2=dye penetration observed between ½ but not beyondthe root-end filling material, 3=dye penetration observed beyond theroot-end filling material and into the canal system. Results wererecorded and submitted to non-parametric Kruskal-Wallis and Mann-WhitneyU-tests.

Chemical Shrinkage—The chemical shrinkage methodology was based on theoriginal work performed by Geiker (19). Modification to Geiker'soriginal work is currently under proposal as the protocol designated todetermine chemical shrinkage of Portland cement for the cement industry,(ASTMCXXXX Test Method for Chemical Shrinkage of Hydraulic Cement Paste)(20). All cement pastes were prepared in accordance to manufacturer'sinstructions at a 0.33 water/cement ratio for groups 1-6 (Group1=PC/H₂O, Group 2=CMMTA, Group 3=MTA/H₂O, Group 4=2% CaCl₂ in MTA, Group5=2% CaCl₂ in Portland cement, and Group 6=1% MC+2% CaCl₂ in Portlandcement). The mass of each empty glass vial (diameter=2.5 cm and height=6cm) was determined to the nearest 0.01 g. Ten grams of cement paste wasplaced in the bottom of each vial using a vibrating table to achieve apaste height between 5 mm and 10 mm in the vial. Mass of the glass vialwas determined with the consolidated cement paste to the nearest 0.0001g. The remainder of the glass vial was then filled to the top withde-aerated water and sealed with a rubber stopper encasing a pipettegraduated in 0.01 ml increments. The respective graduated pipette wasthen filled to the top with de-aerated water with the addition of 1-2drops of hydraulic oil to minimize the evaporative process over the1-week timeframe (FIG. 2). Mass of the vial+capillary tube filled withwater and cement paste was immediately determined to the nearest 0.0001g. The vial was then transferred and placed in a constant temperaturewater bath of 23.0±0.5° C. At 30 minutes (T_(30 m)), the glass vial wasthen removed from the water bath, wiped dry, capillary tube filled toexcess with de-aerated water, and mass determined to the nearest 0.0001g. Additional weight measurements were taken at hourly intervals for thefirst 8 hours (T_(1 h)-T_(8 h)) followed by additional measurements at24 hours (T_(24 h)) and 1 week (T_(168 h)) respectively. Calculation ofthe mass sample was determined as follows:

The mass of cement powder in the vial is given by:

$M_{cement} = \frac{\left( {M_{{vial} + {paste}} - M_{vialempty}} \right)/}{\left( {1.0 + {w/c}} \right)}$

M_(cement)=mass of cement in the vial (g)

M_(vial+paste)=mass of the glass vial with the added cement paste (g)

M_(vialempty)=mass of the empty vial (g)

w/c=water-cement ratio by mass of the prepared paste (0.33)

Once the mass of the cement was calculated, this weight in grams wasincorporated into the following formula to determine the chemicalshrinkage per unit mass at the specific time interval.

The chemical shrinkage per unit mass of cement at time t is computed as:

CS(t)=([M(t)−M(30 min)]/M cement)/ρW

CS(t)=chemical shrinkage at time t (mL/g cement)

M(t)=mass of filled density bottle at time t (g)

ρW=density of water (mL/g) (0.99754 at 23° C.)

M(30 min)=Mass of cement paste at T_(30 m)

To briefly summarize, two 10 gram specimens were run for each cementgroup (Group 1=PC/H₂O, Group 2=CMMTA, Group 3=MTA/ H₂O, Group 4=2% CaCl₂in MTA, Group 5=2% CaCl₂ in Portland cement and Group 6=1% MC+2% CaCl₂in PC) at a 0.33 water/cement ratio. Weight measurements (0.0001 g) weretaken from the shrinkage apparatus initially at 30 minutes (T_(30m))followed by hourly intervals for the first 8 hours (T_(1 h)-T_(8 h)).Subsequent weighing of samples were taken at 24 hours (T_(24 h)) and 1week (T_(168 h)) respectively with the resulting average of each groupbeing reported and statistically examined for differences in chemicalshrinkage per unit mass between groups at the aforementioned specifiedtime intervals (T_(1 h), T_(2 h), T_(3 h), T_(24 h), and T_(168 h)).

Solubility—Degree of solubility of the test samples was determined bythe modified method of ADA/ANSI specification #30 (21) as performed byTorabinejad et al. (22). Briefly, the materials were prepared inaccordance to manufacturer's recommendations. Individual MTA and CMMTAsamples were hand-mixed and transferred into a small disc approximately20 mm×1 5 mm by use of a plastic former and two glass slabs. Mixing andweighing of the samples were performed by a single operator at 23.0±2°C. and a relative humidity of 50±5%. 6 discs of MTA and 8 discs of CMMTAwere prepared and tested. Following fabrication, discs were placed in100% humidity for 21 hours. Discs were removed and stored individuallyin glass jars containing 50 ml of distilled water at 37° C. Thespecimens were then desiccated for 1 hour at 37° C. Individual discswere weighed to the nearest 0.0001 g and placed back into theirrespective glass jars. The water in glass jars were neither changed noradded during the test periods. Desiccation and weighing of samples wereperformed at: 1 day (T₁), 7 days (T₇) and at 21 days (T₂₁). Mean weightsof the specimens were recorded and submitted to non-parametricKruskal-Wallis and Mann-Whitney U-tests to determine statisticaldifferences between weights of the test materials at different timeintervals.

Dispersion Resistance/Washout—The percentage of cement washout of thetest samples was determined by a modified method based on concretestandard test (CRD-C 61-89A) (24). The receiving container and washoutapparatus is shown in FIG. 3. Briefly, two representative 10 gramsamples from each group (Group1=Portland cement, Group2=MTA,Group3=CMMTA) were prepared in accordance to manufacturer's instructionsat a 0.33 water/cement ratio. Each sample was hand-mixed and placed intoa separate receiving container. The cement mixture was tamped down withthe handle of a cement spatula 10-15 times to allow the cement to adhereto the walls of the container. Extruded cement was removed from theoutside of the receiving container allowing the mass of the cement andcontainer to be obtained and recorded to the nearest 0.0001 g (M_(i))Immediately following weight measurement, the receiving container withcement sample was allowed to freely fall through the H₂O to the bottomof a 1000 ml graduated cylinder and sit for 15 seconds. The receivingcontainer was then slowly raised to the top of the graduated cylinder in5±1 seconds, allowed to drain for 2 minutes, air dried carefully toremove excess H₂O but not disrupt the cement, and weighed to the nearest0.0001 g. Mass of the cement remaining in the receiving container wasrecorded as M_(f). Repeated testing was performed three times on thesame cement sample, determining a new M_(f) each time. The M_(f) afterthe final sequence was then calculated as the cumulative loss in massqualifying as the percent washout of the cement (D) demonstrated below.

The washout of the cement is computed as: D=(M_(i)−M_(f) /M _(i))100

D=washout %

M_(i)=mass of sample before initial test

M_(f)=mass of sample after each test Results

Results

Dye Leakage—Microleakage results of all groups are presented in Table 1.Results from group 1 (MTA) showed that 14 of 15 samples (93%) showed anevaluation score of 0 (no leakage) (FIG. 5). From group 2 (CMMTA), 100%of the specimens displayed an evaluation score of 0 (no leakage) (FIG.6). In contrast, 100% of the samples from group 3 (amalgam) displayed anevaluation score of 3 (dye penetration throughout the entire canal). TheKruskal-Wallis test was used to compare differences between all groups.This test revealed a significant difference between the groups (P<0.05).When examining differences within groups, the Mann-Whitney U-test showedthat leakage observed in Group 1 (MTA) was significantly less (P<0.05)than Group 3 (amalgam). Likewise, Group 2 (CMMTA) displayedsignificantly less leakage (P<0.05) than Group 3. There was nosignificant difference noted between Groups 1 (MTA) and 2 (CMMTA)(P<0.05). Positive control samples showed dye leakage throughout theentire canal system, while the negative control samples displayed nosigns of dye penetration.

TABLE 3 Results for root-end filling materials. No. of Evaluation ScoresMaterial Samples 0 1 2 3 MTA/H₂O (Group 1) 15 14 0 0 1 CMMTA (Group 2)15 15 0 0 0 Amalgam (Group 3) 5 0 0 0 5 Positive control† 3 0 0 0 3Negative control‡ 3 3 0 0 0 †Instrumented roots obturated withgutta-percha and sealer; retrograde preparations with no root-endfillings. ‡Instrumented roots obturated with gutta-percha and sealer;entire root surfaces covered with two coats of nail polish.

Chemical Shrinkage—Results from the Kruskal-Wallis test confirmed ourrationale and revealed that there was no significant difference notedbetween groups 1-6 (P<0.05). Furthermore, statistical analysis employedwith Median tests to compare groups at the designated time intervals(T_(1 h), T_(2 h), T_(3 h), T_(24 h), and T_(168 h)) were unable to showa statistically significant difference in mean chemical shrinkagebetween the specimens at the previously mentioned time frames (P<0.05).

In this experiment, we were interested in the amount of shrinkage thatwould occur from time T_(30 m) to time intervals T_(1 h), T_(2 h),T_(3 h), T_(24 h), and T_(168 h). Reasoning for these timeframes wasthat the recommended setting time for MTA is 165 minutes (22). Thus, itis expected that the majority of hydration would be occurring during theinitial three hours for MTA and therefore, chemical shrinkage of thecement would be anticipated to be at its greatest. ASTM guidelines forthis experiment require hourly measurements for the first 8 hours, a 24hour reading, and finally at 1 week.

Graph illustrating chemical shrinkage over 8 hours for samples 1-6.

Solubility—The mean weights (g) of the specimens and standard deviationfor each test material at various time intervals (T_(1 h), T_(7 h),T_(21 h)) are shown in Tables 2 and 3.

TABLE 4 Chemically Modified MTA Solubility Results CMMTA Total Wo Change(Initial in Mass weight) T₁ T₇ T₂₁ (T₀ − T₂₁) Sample 1 0.8925 g 0.8991 g0.9009 g 0.9075 g (+)1.68% Sample 2 0.9479 g 0.9528 g 0.9553 g 0.9640 g(+)1.69% Sample 3 0.9727 g 0.9888 g 0.9899 g 0.9966 g (+)1.66% Sample 40.7681 g 0.7759 g 0.7730 g 0.7756 g (+)2.46% Sample 5 0.9800 g 0.9720 g0.9861 g 0.9850 g (+)0.51% Sample 6 0.8814 g 0.8819 g 0.8896 g 0.8857 g(+)0.49% Sample 7 0.8791 g 0.8771 g 0.8961 g 0.8879 g (+)1.00% Sample 81.0042 g 0.9968 g 1.0130 g 1.0066 g (+)0.24% Mean wt. 0.9157 g ± 0.9181g ± 0.9255 g ± 0.9261 ± (+)1.14% 0.1476 0.1422 0.1499 0.1505 †positivechange in mass = + ‡negative change in mas = −

TABLE 5 MTA Solubility Results MTA Total Wo Change (Initial in Massweight) T₁ T₇ T₂₁ (T₀ − T₂₁) Sample 1 0.8715 g 0.8611 g 0.8797 g 0.8807g (+)1.04% Sample 2 0.7351 g 0.7269 g 0.7467 g 0.7515 g (+)2.18% Sample3 0.8607 g 0.8516 g 0.8716 g 0.8773 g (+)1.66% Sample 4 0.9702 g 0.9569g 0.9602 g 0.9646 g (−)0.58% Sample 5 0.9813 g 0.9579 g 0.9578 g 0.9759g (−)0.55% Sample 6 0.8139 g 0.7920 g 0.7985 g 0.8128 g (−)0.135% Meanwt. 0.8721 g ± 0.8577 g ± 0.8686 g ± 0.8771 g ± (−)0.57% 0.1370 0.13080.1219 0.1256 †positive change in mass = + ‡negative change in mas = −

The change in mass for each of the samples revealed that there was atendency for a positive gain in total mass (+0.024%−+2.46%) with a meangain in mass of 1.14% over the 21 day period for CMMTA samples.Likewise, half of the MTA samples (1-3) revealed a positive change inmass (+1.04%−+2.18%) while samples 4-6 showed a negative change in mass(−0.135%−−0.58%) with an overall mean gain in mass of 0.57% over the 21day period for the MTA samples. When examining differences between thetwo groups, the Mann-Whitney U-test displayed no significant differencesbetween MTA and CMMTA in solubility (P<0.05). Furthermore, statisticalanalysis with the Wilcoxon signed ranks test was unable to show astatistical significant difference when the mean weight of the specimenswere compared at different time intervals (T_(1 h), T_(7 h), T_(21 h))(P<0.05).

Dispersion Resistance/Washout—Weights (g) of each test group withcorresponding repeated measures on washout for Portland cement, MTA, andCMMTA is shown in Tables 4-6 respectively. Results from the Friedmantest used to analyze the amount of cumulative washout revealed asignificant difference observed between groups (P<0.05). However, due tothe small sample size, Post Hoc analysis (Median test) was unable toidentify significant differences within groups.

TABLE 6 Washout Results for Portland Cement Group 1 (Portland cement) MiCumulative (Initial Percent weight) Mf(1) Mf(2) Mf(3) Washout Test #121.3368 g 20.9374 g 20.8175 g 20.7019 g (−)2.9756% Test #2 21.9530 g21.5350 g 21.5632 g 21.4968 g (−)2.0781% Mean 21.6449 g 21.2362 g21.1904 g 21.5994 g (−)2.5269% †positive change in mass = + ‡negativechange in mas = −

TABLE 7 Washout Results for MTA Group 2 (MTA) Mi Cumulative (InitialPercent weight) Mf(1) Mf(2) Mf(3) Washout Test #1 20.9886 g 20.4855 g20.4103 g 20.2767 g (−)3.3918% Test #2 21.4967 g 20.9457 g 20.7365 g20.6874 g (−)3.7647% Mean 21.2427 g 20.7156 g 20.5734 g 20.4821 g(−)3.5783% †positive change in mass = + ‡negative change in mas = −

TABLE 8 Washout Results for Chemically Modified MTA Group 1 (CMMTA) MiCumulative (Initial Percent weight) Mf(1) Mf(2) Mf(3) Washout Test #121.6637 g 21.8742 g 22.0083 g 22.0091 g (−)1.5944% Test #2 22.0066 g22.3133 g 22.2567 g 22.2500 g (−)1.1060% Mean 21.8352 g 22.0938 g22.1325 g 22.1296 g (−)1.3502% †positive change in mass = + ‡negativechange in mas = −

Dye Leakage—An apicoectomy followed by a root-end filling material is acommon endodontic procedure used to rectify recalcitrant periapicalpathosis in teeth where orthograde endodontic therapy has failed andnonsurgical treatment is not an option. One of the properties of anideal root-end filling material is the ability to seal the root canalsystem (2). Dye leakage studies are a quick an effective method toevaluate the sealing ability of root-end filling materials (22). In1989, Kersten and Moorer determined the leakage of methylene blue to becomparable to that of a small bacterial metabolic product of similarmolecular size. Thus, when a filling material does not allow thepenetration of small molecules such as methylene blue, it has thepotential to prevent leakage of larger substances such as bacteria andtheir by-products (24). Under the parameters of this study, leakage wasquantified with the use of a Likert four-point scale in which 0=no dyepenetration observed, 1=dye penetration observed up to 1 of the cavitydepth, 2=dye penetration observed between 1/2 but not beyond root-endfilling material placement, and 3=dye penetration observed beyond thefilling material and into the canal system. Thus, greater disparity froma score of zero directly reflects the ability of the root-end filling toadequately seal the dentin/material interface. Graphical representationof leakage scores obtained over 72 hours is presented in Table 1. Fromthis table, we were able to conclude that the greatest disparityoccurred between amalgam and CMMTA groups. A similar contrast was alsoevident between the MTA and amalgam groups. However, there was nosignificant difference noted in leakage between MTA and CMMTA groups.

Our results indicate that the CMMTA (1% methylcellulose+2% CaCl₂ in MTA)was comparable to the unaltered MTA (MTA/H₂O) in preventing dyepenetration beyond the extent of the material. Therefore, the additivesplaced into MTA had no significant effect on its sealing properties. Infact, the chemically modified MTA showed no evidence of leakage in all15 specimens.

Chemical Shrinkage—Numerous properties of cementitious materials arecontrolled by their initial hydration rate (early-age strengthdevelopment, heat release, and crack resistance). A direct method foranalysis of the cement's initial hydration rate is by quantifying thechemical shrinkage of the cement paste during its hydration. As cementhydrates, the hydration products occupy less volume than the initialreacting materials (cement and water). As a result of this volumechange, a hydrating cement paste will absorb water, if available fromits immediate surroundings. At early times this water absorption is indirect proportion to the amount of hydration that has occurred (25).

It has been generally considered that a potential root-end fillingmaterial should set as soon as it is placed in a root-end cavity withoutsignificant shrinkage. This would allow for dimensional stability of thematerial after placement and less time for an unset material to be incontact with periapical tissues. The incorporation of 1%methylcellulose+2% CaCl₂ into MTA by Ber. (18) has demonstrated to showpromise to rectify some of MTA's potential shortcomings as a root-endfilling material (long setting time and poor handling characteristics).A detrimental effect of calcium chloride is drying shrinkage (26). Thisstudy was undertaken to determine if the incorporated additives (namelyCaCl₂) into MTA significantly affected the chemical shrinkage propertiesof MTA.

Statistical analysis in the mean amount of chemical shrinkage occurringover 1 week (168 hours) for each of the six groups revealed nosignificant difference between groups at any of the determined timeintervals (P<0.05). As illustrated in FIG. 8, specimens with thegreatest to the least amount of chemical shrinkage displayed over 1 weekis represented as follows: Group 5 (2% CaCl₂ in PC)>Group 6 (1% MC+2%CaCl₂ in PC)>Group 1 (PC/H₂O)>Group 4 (2% CaCl₂ in MTA)>Group 2(CMMTA)>Group 3 (MTA/H₂O). We expanded the graph to provide a clearerrepresentation of specific trends for each specimen tested relative toearly age shrinkage (T₀-T₈) (FIG. 9). Both figures illustrate aconsistent increase in chemical shrinkage for each of the specimenstested over time. Likewise, the addition of 2% calcium chloride revealeda propensity to increase the chemical shrinkage rate. This is expected,since calcium chloride is used as an accelerant to increase thehydration process and provide early-age strength. Nonetheless,statistical analysis was able to demonstrate no significant amount ofshrinkage between MTA and CMMTA mean samples.

These results have demonstrated that unique to the dental sector andunlike in the cement industry, small quantities (usually <1 gram) of MTAmixed at a 3:1 w/c ratio placed in intimate contact with periapicaltissues which provides 100% humidity within an aqueous environment willenable and maintain saturation of the material and prevent a significantamount of autogenous or drying shrinkage.

Solubility—Root-end filling materials used during periapical surgery areroutinely placed in intimate contact with inflamed or infected areas ofthe periodontium. It is therefore essential that the root-end fillingmaterial be given every opportunity to maintain its apical seal andresist dissolution while in the presence of moisture/blood or lowered pHof the involved area. Torabinejad et al. was able to demonstrate thatMTA leaked significantly less than amalgam, Super EBA and IRM in thepresence of blood, and they observed that the presence or absence ofblood had no significant effect on the amount of leakage of the material(27). The rationale for this is that MTA beneficial properties arerealized with the added moisture from blood within the surgical siteduring the hydration process to initiate the initial seal. Theliterature states the presence of periradicular inflammation may providean acidic pH of 5.5 and this lowered pH may alter the physicalproperties of MTA to inhibit setting reactions, affect adhesion, orincrease solubility of the material (28). A study performed by Roy etal. was able to demonstrate that the sealing ability of freshly mixedMTA was not affected in an acidic environment (pH 5.0) (29). Conversely,a study performed by Lee et al. was able to make evident that an acidenvironment of pH 5 adversely affected the physical properties and thehydration behavior of MTA by retarding the dissolution of reactants,(C₃S, C₂S, and C₃A) therefore decreasing the production of Portlanditecrystals. Furthermore, SEM and XRD analysis also revealed that thelowered pH had potentiated a decreased hardness value of MTA withdissolution of surface crystals (30).

The inventors observed that the addition of 1% MC and 2% CaCl₂ into MTAhad no detrimental effects on the material's solubility. Under theparameters used in this example, all specimens were immersed indistilled H₂O for 21 days to provide an adequate timeframe to identifytrends in the initial solubility that may affect long-term results.Thus, if the material would show any initial dissolution, there would bea chance that the marginal seal has been disrupted and the potential forleakage to occur.

From the observations, it appears that specimens from both CMMTA and MTAgroups showed no or minimal signs of solubility in water over theobservation time. In fact, CMMTA and MTA groups both demonstrated meanincreases in water absorption over the 21 day period respectively(+1.14% and +0.57%). Our results were somewhat surprising to see apositive change in mean mass for both groups over this timeframe. Onemay direct this discrepancy to standard measuring error where thespecimens were weighed to 0.0001 grams. It is also plausible,methylcellulose, which is traditionally used as a bulking agent in themarketplace, may have potentially absorbed additional water into thecement during the hydration process adding to the higher mean increasein weight of CMMTA. Nonetheless, these results are in agreement with astudy performed by Torabinejad, (22) who concluded that MTA, Super-EBA,and amalgam showed no signs of solubility at 21 days.

Clinically, there is no standard method for predictably measuring themanufacturer's recommended 3:1 w/c ratios for MTA. Fridland (31) wasable to demonstrate that the degree of solubility in MTA increased asw/c ratio increased. Therefore, the amount of water used in preparingthe mix has a direct effect on solubility when the material is incontact with an aqueous environment. This increase in solubility has thepotential to affect the long-term seal that can essentially lower theoverall success of the endodontic procedure.

Our data is in opposition to a recent study performed by Fridland (32).This long-term study measured solubility over 78 days with varying w/cratios. The authors concluded that MTA with a 0.33 w/c ratio over 78days revealed a 24.04% cumulative solubility of the material's initialdry weight. The disparity in solubility results between studies couldhave resulted from differences in measurement methodology. Fridland etal. calculated solubility according to an amalgamation of ISO 6876standard (33) and ADA Specification #30 (34). In essence, Fridland etal. used an indirect weight measurement to determine the solubility ofMTA. These authors used values from the weighted residues as apercentage of the initial dry weight of the specimens. In contrast, ourmethodology mirrored a study performed by Torabinejad, (22) who used amodification to ADA Specification #30 using direct measurement of thespecimens at the dedicated time intervals.

Dispersion Resistance/Washout—During periapical surgery, root-endfilling materials are inevitably exposed to periapical tissues andfluids. This continuous moisture contamination may complicate theplacement of an effective seal and place the material at risk to washoutof the material. This is particularly relevant for freshly placed MTAbecause of its lengthy setting time (165 minutes) (22).

MTA seems to have similar vulnerabilities to washout as Portland cementwhen placed in aqueous environments with prolonged setting times. Thecement industry routinely deals with wet conditions (underwater concreteplacement) that can potentially affect the properties of the material,not unlike conditions encountered during periapical surgery. For adiscussion of how the cement industry addresses problems of wetconditions, see Concrete Construction Engineering Handbook, E. Nawy,ed., New York, CRC Press, 1997; Concrete Construction Handbook, J.Dobrowski, 4th ed., New York, McGraw-Hill, Inc., 1998; and Kosmatka andPanarese, Design and Control of Concrete Mixtures, 13th ed., PortlandCement Association, Skokie, Ill., 1988, all of which are hereinincorporated by reference. To address these problems for dentalapplication, an anti-washout mixture (methylcellulose) is added to thecement to facilitate a more cohesive cement. The addition of thisadditive increases the viscosity of the water used in the mixture,therefore, producing a more thixotropic material to resist washout.Clinically, most of the disintegration of the cement will initiallyoccur during the placement of the material and not once it has set. Thatis why the addition of this cohesive antiwashout material may inhibitthe dispersion of material from the cavity both during placement and aswell as the first few hours of setting.

The inventors (18) have adopted the cement industry's solutions to theseproblems with the addition of 1% methylcellulose+2% CaCl₂ in MTA. Theinventors evaluated in this example whether the chemically modified MTAhas provided added benefits to the parent cement (MTA) in terms ofwashout resistance. The results obtained in this study landed within thetypical performance requirements for allowable washout (<6-12%) ofunderwater concrete for all of the specimens tested (34). Indeed, ourresults from the Friedman test used to analyze cumulative washoutrevealed a significant difference observed between groups (P<0.05). Whenevaluating the data mathematically, one could arrive at a conclusionthat the significant difference in mean cumulative washout was betweenGroup 2 (MTA=−3.57%) and Group 3 (CMMTA=+1.34%). As in the solubilitystudy, we would expect to see a negative washout value for CMMTA. Thepositive cumulative washout for CMMTA could possibly be explained bystandard measuring error of the materials during the weight measurementprocess or inadequate removal of H₂O from the receiving container priorto measurement.

In conclusion, the data presented in this example support our positionthat the addition of 1% MC+2% CaCl₂ into MTA has not deleteriouslyaltered any of the parent cement's additional physical properties(marginal leakage, chemical shrinkage, cement solubility, and washoutresistance). On the contrary, the results from the four studies testingthe physical properties of CMMTA have concluded: Dye leakage resultsdemonstrated that there was no statistically significant differencenoted between CMMTA and MTA samples (P<0.05). In addition, we were ableto demonstrate significantly less leakage between the CMMTA and MTAgroups compared to amalgam (P<0.05). Chemical shrinkage results reportedno statistically significant difference noted between any of the groupsat any of the designated timeframes (T₁, T₂, T₃, T₂₄, T_(w)). Moreimportantly, we were able to show no statistically significantdifference in mean chemical shrinkage between CMMTA and MTA samples atany of the designated time intervals of the specimens (P<0.05). Cementsolubility results revealed no statistically significant differencebetween CMMTA and MTA groups (P<0.05). Furthermore, we were able to showno significant difference between weights of the test materials atdifferent time intervals. Modified washout tests indicated a significantdifference observed between groups 1-3 (P<0.05). Data obtained from thestudy demonstrated CMMTA as having the most mean cumulative washoutresistance while MTA displayed the least cumulative washout resistance.However, there were no significant differences noted between these twogroups (P<0.05).

The following references are cited throughout this section using therelated parenthetical numbering system. The references are incorporatedherein by reference. Applicant reserves the right to challenge theveracity of statements made therein.

1) Sarkar N K, Caicedo R, Ritwik P, Moiseyeva R, Kawashima I.Physicochemical basis of the biologic properties of mineral trioxideaggregate. J Endod. 2005; 31:97-100.

2) Gartner A H, Dom S O. Advances in endodontic surgery. Dent Clin NorthAm 1992; 36:357-78.

3) Koh E T, Torabinejad M, Pitt Ford T R, Brady K, McDonald F. Mineraltrioxide aggregate stimulates a biological response in humanosteoblasts. J Biomed Mater Res. 1997; 37:432-9.

4) Koh E T, McDonald F, Pitt Ford T R, Torabinejad M. Cellular responseto Mineral Trioxide Aggregate. J Endod 1998; 24:543-7.

5) Torabinejad M, Hong C U, Pitt Ford T R, Kaiyawasama S P. Tissuereaction to implanted super-EBA and mineral trioxide aggregate in themandible of guinea pigs: a preliminary report. J Endod 1995; 21:569-71.

6) Torabinejad M, Ford T R, Abedi H R, Kariyawasama S P, Tang H M.Tissue reaction to implanted root-end filling materials in the tibia andmandible of guinea pigs. J Endod 1998; 24:468-71.

7) Pitt Ford T R, Torabinejad M, Abedi H R, Bakland L K, Kariyawasama SP. Using mineral trioxide aggregate as a pulp-capping material. J AmDent Assoc 1996; 127:1491-4.

8) Osorio R M, Hefti A, Vertucci F J, Shawley A L. Cytotoxicity ofendodontic materials. J Endod 1998; 24:91-6.

9) Keiser K, Johnson C C, Tipton D A. Cytotoxicity of mineral trioxideaggregate using human periodontal ligament fibroblasts. J Endod 2000;26:288-91.

10) Torabinejad M, Rastegar A F, Kettering J D, Pitt Ford T R. Bacterialleakage of mineral trioxide aggregate as a root-end filling material. JEndod 1995; 21:109-12.

11) Wu M K, Kontakiotis E G, Wesselink P R. Long-term seal provided bysome root-end filling materials. J Endod. 1998; 24:557-60.

12) Torabinejad M, Watson T F, Pitt Ford T R. Sealing ability of amineral trioxide aggregate when used as a root end filling material. JEndod. 1993; 19:591-5.

13) Martell B, Chandler N P. Electrical and dye leakage comparison ofthree root-end restorative materials. Quintessence Int. 2002; 33:30-4.

14) Torabinejad M, Higa R K, McKendry D J, Pitt Ford T R. Dye leakage offour root end filling materials: effects of blood contamination. J Endod1994; 20:159-63.

15) PROROOT MTA, Product Literature, Dentsply Tulsa Dental, Tulsa, Okla.74136.

16) Deal B, Wenkus C, Johnson B, Fayad M. Chemical and physicalproperties of MTA, Portland cement, and a new experimental material,fast-set MTA. J Endod 2002; 28:252.

17) Lee E S. A new mineral trioxide aggregate root-end fillingtechnique. J Endod 2000; 26:764-5.

18) Ber, B S. “Manipulation of Handling Characteristics of MTA,”Master's Thesis, Saint Louis University, 2004.

19) M. Geiker, Studies of Portland Cement Hydration: Measurements ofChemical Shrinkage and a Systematic Evaluation of Hydration Curves byMeans of the Dispersion Model. Ph. D. Thesis, Technical University ofDenmark, 1983.

20) Proposed test method ASTM CXXXX Test method for chemical shrinkageof hydraulic cement paste. ASTM Committee C-1. Subcommittee C01.31 onvolume change.

21) ANSI/ADA. Revised American National Standard/American DentalAssociation Specification No. 30 for dental zinc oxide eugenol cementsand zinc oxide noneugenol cement 7.5, 2000.

22) Torabinejad M, Hong C U, McDonald F, Pitt Ford T R. Physical andchemical properties of a new root-end filling material. J Endod 1995;21:349-53.

23) Proposed test method ASTM CXXXX Test method for chemical shrinkageof hydraulic cement paste. ASTM Committee C-1. Subcommittee C01.31 onvolume change.

24) Kersten H W, Moorer W R. Particles and molecules in endodonticleakage. Int Endod J. 1989; 22:118-24.

25) Parrott L. J, Geiker M, Gutteridge W. A., Killoh D., MonitoringPortland cement hydration: comparison of methods. Cement and ConcreteResearch. 1990; 20:919-926.

26) Kosmatka, Steven H., and Panarese, William C. Design and Control ofConcrete Mixtures, 13th ed., PortlandCement Association, Skokie, Ill.1988.

27) Torabinejad M, Higa R K, McKendry D J, Pitt Ford T R. Dye leakage offour root end filling materials: effects of blood contamination. J Endod1994; 20:159-63.

28) Malamed S. Chapter 16. In: Local anesthetic considerations in dentalspecialties: handbook of local anesthesia. 4th edn. St. Louis: Mosby;1997; p. 232.

29) Roy C O, Jeansonne B G, Gerrets T F. Effect of an acid environmenton leakage of root-end filling materials. J Endod 2001; 27:7-8.

30) Lee Y L, Lee B S, Lin F H, Yun Lin A, Lan W H, Lin C P. Effects ofphysiological environments on the hydration behavior of mineral trioxideaggregate. Biomaterials. 2004; 25:787-93.

31) Fridland M, Rosado R. Mineral trioxide aggregate (MTA) solubilityand porosity with different water-to-powder ratios. J Endod. 2003;29:814-7.

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33) International Organization for Standardization. Specification fordental root canal sealing materials. ISO 6876. London: British StandardsInstitution, 2001.

34) ANSI/ADA. Revised American National Standard/American DentalAssociation Specification No. 30 for dental zinc oxide eugenol cementsand zinc oxide noneugenol cement 7.5, 2000.

35) Department of the Army EC 1110-2-6052. U.S. Army Corps of EngineersCECW-EI Washington, D.C. 20314-1000. 2001; Appendix B-6.

1. A dental repair composition comprising: a mineral trioxide aggregate,a divalent cation halogen salt, and a cellulose-derivative polymer. 2.The dental repair composition of claim 1, wherein the divalent cationhalogen salt is selected from the group consisting of calcium chloride,magnesium chloride, sodium chloride, and potassium chloride.
 3. Thedental repair composition of claim 1, wherein the divalent cationhalogen salt is from about 0.1% (w/w) to about 10% (w/w).
 4. The dentalrepair composition of claim 1, wherein the divalent cation halogen saltis about 2% (w/w).
 5. The dental repair composition of claim 1, whereinthe cellulose-derivative polymer is selected from the group consistingof methyl cellulose, ethyl cellulose, ethyl methyl cellulose,hydroxyethyl cellulose, hydroxyethyl methyl cellulose, hydroxypropylcellulose, ethyl hydroxyethyl cellulose, and carboxymethyl cellulose. 6.The dental repair composition of claim 1, wherein thecellulose-derivative polymer is from about 0.1% (w/w) to about 10%(w/w).
 7. The dental repair composition of claim 1, wherein thecellulose-derivative polymer is about 1% (w/w).
 8. The dental repaircomposition of claim 1 comprising a setting time of less than 200minutes.
 9. The dental repair composition of claim 1 comprising aviscosity of from about 50,000,000 centipoise to about 150,000,000centipoise.
 10. The dental repair composition of claim 1 comprising acompressive strength measured at about 24 hours of from about 20 MPa toabout 30 Mpa.
 11. The dental repair composition of claim 1 comprising acompressive strength measured at about 3 weeks of from about 22 MPa toabout 36 Mpa.
 12. A dental repair composition prepared by a processcomprising: preparing a divalent cation halogen salt solution; warming aportion of the divalent cation halogen salt solution to a temperature ofbetween about 60° C. to about 90° C. to prepare a warmed divalent cationhalogen salt solution; mixing a cellulose-derivative polymer with thewarmed divalent cation halogen salt solution to prepare a warmeddivalent cation halogen salt-cellulose polymer solution; mixing aremaining portion of the divalent cation halogen salt solution with thewarmed divalent cation halogen salt-cellulose-derivative polymersolution; cooling warmed divalent cation halogensalt-cellulose-derivative polymer solution to a temperature of betweenabout 0° C. to about 10° C. to form a gel; mixing the gel with a mineraltrioxide aggregate solution to prepare the dental repair composition.13. The dental repair composition of claim 12, wherein the divalentcation halogen salt is selected from the group consisting of calciumchloride, magnesium chloride, sodium chloride, and potassium chloride.14. The dental repair composition of claim 12, wherein the divalentcation halogen salt is from about 0.1% (w/w) to about 10% (w/w).
 15. Thedental repair composition of claim 12, wherein the divalent cationhalogen salt is about 2% (w/w).
 16. The dental repair composition ofclaim 12, wherein the cellulose-derivative polymer is selected from thegroup consisting of methyl cellulose, ethyl cellulose, ethyl methylcellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose,hydroxypropyl cellulose, ethyl hydroxyethyl cellulose, and carboxymethylcellulose.
 17. The dental repair composition of claim 12, wherein thecellulose-derivative polymer is from about 0.1% (w/w) to about 10%(w/w).
 18. The dental repair composition of claim 12, wherein thecellulose-derivative polymer is about 1% (w/w).
 19. A dental repair kitcomprising a first container a mineral trioxide aggregate, in a secondcontainer a divalent cation halogen salt, and in a third container acellulose-derivative polymer.
 20. The dental repair kit of claim 19further comprising instructions for making a dental repair compositioncomprising: a mineral trioxide aggregate, a divalent cation halogensalt, and a cellulose-derivative polymer.